Synthesis of structurally stable MCM-48 using mixed surfactants as co-template and adsorption of vitamin B12 on the mesoporous MCM-48

Abstract

Structurally stable MCM-48 mesoporous silica has been facilely synthesized by a new method using mixtures of cationic surfactant cetyltrimethylammonium bromide (CTAB) and nonionic poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) triblock copolymer surfactant (Pluronic P123) as co-template. For comparison purpose, the cubic MCM-48 material was also prepared via only CTAB as the structure-directing agent under the same synthesis conditions. The products obtained by different templating methods were thoroughly characterized by XRD, N 2 sorption, TEM and FT-IR spectroscopy. The results showed that the synergism effects of the binary system of cationic and nonionic surfactants favored the formation of cubic MCM-48 with extremely low molar ratio of CTAB to SiO 2 (0.125:1). From the FT-IR spectra, the stronger intensity of Si–O–Si peaks and the reduction in the absorbance of the Si–OH stretch band of the product obtained via mixed surfactants, and combination of XRD, N 2 sorption, TEM, all measurement results clearly proved its structural stability. The improvement of the stability is attributed to the introduction of P123 resulting in pore wall thickened and a Si–OH group reduction on the pore surface. The adsorption of vitamin B12 on the mesoporous MCM-48 obtained by different templating methods were studied. The MCM-48 obtained via mixed surfactants showed higher adsorption capacity compared with the one obtained via the single cationic CTAB templating route, which is associated with proper amount of Si–OH group on the pore surface and slit-shape pore structure.